It is known to provide a decoupling mechanism on an accessory, such as an alternator, that is driven by a belt from an engine in a vehicle. Such a decoupling mechanism, which may be referred to as a decoupler, permits the associated accessory to operate temporarily at a speed that is different than the speed of the belt. For example, when there is a sudden stoppage of the belt when the belt was running and driving rotation of the alternator shaft, the decoupler permits the alternator shaft to continue rotating temporarily as a result of inertia until it decelerates to a stop as a result of drag, thereby reducing the stress on the alternator shaft. As another example, the decoupler permits the alternator shaft to rotate at a relatively constant speed even though the crankshaft from the engine undergoes a cycle of decelerations and accelerations associated with the movement of the pistons.
Such a decoupler is a valuable additions to the powertrain of the vehicle. However, it can be costly to manufacture for various reasons. One example that drives up its cost is the pulley that is included with it. In certain decouplers the pulley is typically made from steel because it is engaged with the wrap spring that is in the decoupler. The pulley may have to coated for appearance reasons. The interior surface of the pulley, however, is machined to have selected dimensions with very tight tolerances to provide predictability in its engagement with the wrap spring. Thus, coatings, which typically have a relatively high variability in their thickness, cannot typically be applied to its interior surface that engages the wrap spring. Thus the coating process is made more difficult and expensive than it would otherwise be. Additionally, the coating itself can be prone to scratches, which could cause the entire decoupler to be rejected upon inspection.
Other problems arise when a decoupler with a wrap spring is used in conjunction with a BAS (Belt-Alternator-Start) system on a vehicle. In such a system, the alternator is driven as a motor and is used to drive the belt, so that the belt drives the engine's crankshaft, in order to start the engine. The wrap spring, however, prevents the alternator shaft from driving the pulley however, and so a separate electric clutch has been proposed to overcome this issue. Such clutches are expensive and complex however.
There is a continuing need to reduce their cost, to improve their operating life, to reduce their complexity and to simplify their manufacture. It would thus be beneficial to provide a decoupler that addresses one or more of these continuing needs.